Posted
by
kdawson
on Tuesday May 20, 2008 @04:34PM
from the hiding-in-plain-sight dept.

esocid sends along the news that scientists believe they have found about half the missing matter in the universe. The matter we can see is only about 1/8 of the total baryonic matter believed to exist (and only 1/200 the mass-energy of the visible universe). This missing matter is not to be confused with "dark matter," which is thought to be non-baryonic. The missing stuff has been found in the intergalactic medium that extends essentially throughout all of space, from just outside our galaxy to the most distant regions of space. "'We think we are seeing the strands of a web-like structure that forms the backbone of the universe,' Mike Shull of the University of Colorado explained. 'What we are confirming in detail is that intergalactic space, which intuitively might seem to be empty, is in fact the reservoir for most of the normal, baryonic matter in the universe.'"

I knew someone was going to make an ether comment. The luminiferous ether was the hypothecial medium that electromagnetic waves (including light) traveled through. It was hypothesized because, at the time, there were no known waves that traveled without a medium. However, the ether was disproven, and it was shown that EM waves travel without a medium. What's mentioned in the article is not ether.

Yup, Disproven.Because Einstein got everything perfect (cosmological constant)And light (which may or may not have mass) is bent by gravity (bending space time)

Wouldn't it make more sense to go with an aether theory?

You say light travels at the same speed regardless of direction or relative motion? I say bunk requiring some very sophisticated manipulations of time and space (Lorentz contractions) What's wrong with the 'entrained aether' theory? What, you never heard of frame-dragging?

Because Einstein got everything perfect (cosmological constant)
And light (which may or may not have mass) is bent by gravity (bending space time)
Wouldn't it make more sense to go with an aether theory?

Not when it's wrong. I'm sorry if reality is too complicated for you, but that's your problem not ours.

You say light travels at the same speed regardless of direction or relative motion? I say bunk requiring some very sophisticated manipulations of time and space (Lorentz contractions) What's wrong with the 'entrained aether' theory? What, you never heard of frame-dragging?

No, light travels at a constant speed in a vacuum. It's speed can be different based on a whole variety of factors.

Gravitational lensing? How about gravity increasing the optical density of the aether?

disclaimer: I am a physics graduate.
EM waves consist of an oscillating electric field (along with its magnetic counterpart)...what was that electric field doing before it started oscillating? It was probably a static field. Think about this, if I have a magnet and I wiggle it around, the disturbance in the field of the magnet travels outward from the source at the speed of light, but the field was there but merely static initially. Same deal with gravity waves. So whether the local field is static or osci

I've got a question for a physics graduate or anybody who can answer it. After reading for the thousandth time about all the ionized gasses in space, I suddenly began to wonder how many electrons were created in the Big Bang? Like - are there enough electrons for every atomic nucleus to fill it's shells - if they weren't ionized? Now, that seems improbable, because an enormous amount of matter was created after the Big Bang - created in stars and super novae. Then this matter that was created - were electro

Thanks! I found the answer, and read some very interesting discussion in the links you provided. Interesting that though I have been reading about physics and astronomy for many years, I have never run into this kind of discussion before...

"The electromagnetic force is so strong that if the universe had even a slight net charge, electric and magnetic fields should dominate the structure of our universe. But it doesn't -- gravity does. And gravity, believe it or not, is a very weak force.
There are other effects that electric and magnetic fields would have on light, and we simply do not see these effects."

"If a gas in ionized it simply means that some electrons have separated from the constituent atoms (or molecules) that make up the gas leaving positively charged atoms/molecules and negatively charged electron. However they are still mixed together in the same gas, the 'separation' that you assume does not exist. The positive and negative charges still mingle in the same space. Even if you took a very small volume (the size of a grain of sand) of an ionized gas the overall charge is still neutral."

disclaimer: I am a physics graduate.
EM waves consist of an oscillating electric field (along with its magnetic counterpart)...what was that electric field doing before it started oscillating? It was probably a static field. Think about this, if I have a magnet and I wiggle it around, the disturbance in the field of the magnet travels outward from the source at the speed of light, but the field was there but merely static initially. Same deal with gravity waves. So whether the local field is static or oscillating, it was always previously existent regardless of its state. While I don't believe in the luminiferous aether either I also don't see how a field disturbance (electric, magnetic or gravitational) can travel through something that isn't there. I hope people can see what I'm talking about because while relativity and the aether don't make sense on their own, there are aspects of both theories that accurately describe reality and as is often the case in modeling reality it is not often a case of either / or, eg wave-particle duality in describing the sub-atomic world.

That wave is not static, it's vibrational displacement is assumed inert/static because we have no way of approximating such a minute difference in change, for now.

I'm taking a grad-level course in optical properties of condensed matter, and one of the things we study is how EM propagation is slowed by atomic dipole formation in polarization from photonic fields. It would be interesting if it were the case that the vacuum could be demonstrated to have, at the quantum level, some degree of spontaneous polarization in a field, and since there's always a field (even if perhaps self-induced from uncertainty foam), you could somehow make an analogy to the concept of the a

Consider pure EM radiation, such as that given off by a black-body. Prior to giving off radiation, there is no electric or magnetic field. The sum over all space of the E and M fields when radiation is being given off is still zero. (Makes sense: we've created no charges and no currents, so there should be no static E or M fields.)Bear in mind that "the field is oscillating" isn't really a clear description. This implies that the field is the medium, but it's not. Consider waves in a medium -- say, water. I

Wouldn't it make more sense to go with an aether theory? [...] How about gravity increasing the optical density of the aether?

The problem with ether theories is mainly the Michelson-Morley experiment. Are there ether theories which avoid the MM pitfall? Sort of. The Polarizable Vacuum [wikipedia.org] (PV) is a very interesting theory along the lines of what the the above poster suggested. Instead of matter bending some mysterious "ether", as in ether theories, or bending space-time, as in relativity, matter instead affects the electric and magnetic permeability of space, which causes light to behave as if it were passing through a medium with a higher dialectric constant. From that simple assumption, we can almost rederive full general relativity (GR) wherein electromagnetic equations produce gravitational effects. Gravity is electromagnetism! PV has since been disproven, but it's still a stunningly simple way to think about gravitation in terms of electromagnetism.

I think the Michelson-Morley experiment fails due to it's assumption that the observation device isn't at the center of the universe. The way I look at it, the point of observation (measurement) very well COULD be considered the center of the universe. Pardon my non-university foolishness, but don't waveforms collapse outward from the point of measurement?Not that I'm an outspoken advocate of aether theory or anything, I've just been bugged by that little thought since high school, and this seemed like a

It's not quite like that... Quantum states' collapse is barely real in the sense that we know it. In particular, it doesn't carry information - so the experiments we already have, which indicate that what we call collapse is a non-local phenomenon (carries faster than the speed of light, possibly instantly), don't contradict special relativity.

Yes, you read correctly - to all our best measurements, collapse appears instantaneous, not like a propagating change in a wave.

Wave function collapse is a much more controversial thing than the existence or non-existence of the ether. Basically, it's the only non-unitary, non-differentiable, discontinuous part of quantum mechanics. Oh, and it violates special relativity, though that might count for less given the topic of discussion here. There are various suggestions (such as many-worlds theories) that might avoid the need for this artificial wavefunction collapse altogether.Back to the topic at hand, the interesting thing with

Why does wavefunction collapse violate SR? SR prohibits information traveling faster than light. The no-communication theorem http://en.wikipedia.org/wiki/No-communication_theorem [wikipedia.org] (I'd always called this the no-signaling theorem) leads to the no-cloning theorem http://en.wikipedia.org/wiki/No_cloning_theorem [wikipedia.org] so if you like, SR "explains" the no-cloning theorem. (The no-cloning theorem still allows a cloning fidelity of 5/6. Last I saw, fidelities of 0.81 had been achieved)

Back to the topic at hand, the interesting thing with special relativity is that while it was created based on the results of the Michelson-Morley experiment, it doesn't actually "explain" that experiment.

Maxwell's equations (see sig) predict that light will propagate with a speed c independent of frame. Einstein had a choice, Newton was wrong or Maxwell was wrong. A non-null result from the MM experiment would invalidate Maxwell's equations.

Michelson-Morley was an important part of it, but it was Einstein that finally killed it off by proving that waves and particles aren't as seperate as they appear to be, and thus ether is unnecessary. A few stodgy professors hung on for a while, but they eventually retired/died off without convincing very many of their students.

I've been amuzed for years that the actual experimental equipment being built to detect gravity waves is basically the same (though far more precise) as in the Michelson-Morley experiment, but we expect to see the opposite result. In other words, the result we're looking for would have looked a whole lot like ether if found 100 years ago.

Not exactly... The MM experiment predicted a phase shift when the optics table was rotated. It wasn't time-dependent. The phase shifts expected by LIGO/LISA are sporadic events that should only be sensitive to huge events such as black hole creation or neutron star mergers. They won't vary with the orientation of the plane of the interferometer, and they won't be constant in time either.

Well, if you assume that the Earth moves through such a medium as it orbits the Sun, you can look for that, as you can tell there's a medium when you move relative to it - which was the Michelson-Morley experiment [virginia.edu].

Always wondered why a simple explanation like dust never took hold, and everyone started talking about invisible matter to explain what should be there.

We know that there is some sort of matter missing due to weird graviational interactions. We also know that according our measurements of the cosmic microwave background, this matter doesn't exist, i.e., this matter doesn't interact with electromagnetic fields. That's why it's not normal baryonic matter.

Therefore, we say that there must be dark matter. Plain old dust would have showed up in our readings of the CMB.

Close. A free proton and ionized hydrogen are the same. (A proton in the nucleus of a non-hydrogen atom is different.) There seem to be different standards for when which term is used, but I usually see free protons referred to as hydrogen ions. (Obviously if you ionize hydrogen, you should call the result hydrogen ions.)

Well, dust is not dark matter. There's other matter besides baryonic matter. There's a great picture on wikipedia that 'shows' dark matter. The debate on dark matter is how much it exists and its exact nature, not whether it exists.

Fine, find some sort of matter interacts gravitationally with the observable universe but not electromagnetically, and call it whatever you want when you do. We'll be over here calling it non-baryonic matter, or dark matter.

Fine, find some sort of matter interacts gravitationally with the observable universe but not electromagnetically, and call it whatever you want when you do. We'll be over here calling it non-baryonic matter, or dark matter

Wouldn't a big blob of noble gases in the galaxies and then some sort of interstellar / undiscovered physics to mute the spectra do the trick?

I'm not an astronomer, but I thought the deal with dark matter is that it was necessary to explain the measured rotational speed of the galaxies -

I highly recommend to you the wikipedia article on the subject. The short form is that we've covered all of the other bases with dark matter. We know that not only is there mass out there that we can't detect, there's a staggering amount of it. Most of the mass in the universe, in fact. If it were normal matter, it would be dense enough for star formation. Things behave wildly differently than they're supposed to, and short of revising our theory of gravitation in a complex and inconsistent way, we are left

The short form is that we've covered all of the other bases with dark matter.

I read it... very interesting. It seems to me though, that "covered all the bases" really means "researched as much as we think we can with the tools that we have." It's like, you can't just go out there and measure stuff, you know. A lot of it is weighing subtle things together and making a case, until someone does something really amazing and discovers that background noise on a satellite antenna is actually radiation from the

The universe is a pretty cool place, really. Although in the case of the CMBR, it was theorized to exist before it was discovered experimentally.

what if space time isn't the flat sheet distorted like is thought

Well, actually, we've been able to measure that. Here's a summary [nasa.gov], but we're pretty sure that the universe is flat (parallel lines will never converge), to within a 2% margin of error. Neat work, that.

I have pretty much the same sense of wonder and awe when faced with the incredible complexity of the universe. It's such an incredible, marvellous thing

I'm not an astrophysicist, but the last I've read on the subject implied that the possibility of MOND being correct was unlikely at best, and purely specious at worst. The Bullet Cluster especially seems like it would require a great deal of explanation. As far as I know, while it's not a settled issue, the preponderance of evidence at this time supports the existence of dark matter.

To which the answer is: NO, this is not the dark matter. This does not explain the dark matter. This is unrelated to dark matter.

Which is perfectly clear if you RTFA before posting. Or even payed close attention when reading the summary. I realize this are a bit much to ask. But when you post in ignorance, and someone says, "No, RTFA"... At that point, before you argue with them, for the love of God, RTFA!

Ok, sure I did. But I think you missed the point. I wasn't saying anything was dark matter. I'm saying we found more real matter. Those generous question marks were my pokes against people who want dark matter to explain everything away when perfectly normal matter will suffice.

Except there aren't people like that. We knew this normal matter existed, we just didn't know where it was.

Every time we talk about something new being found in the universe, someone likes to say, "Oh look at those stupid astronomers, making up stuff no one can prove. There never was any dark matter." I know that's not what you specifically said, but by bringing it into the conversation and conflating this observation with theories of dark matter, you essentially did the same thing. Your basi

Every time we talk about something new being found in the universe, someone likes to say, "Oh look at those stupid astronomers, making up stuff no one can prove

That statement is essentially true. The best you can ever know about the universe is by inference. Standard candles are an approximation and you aren't really able to prove anything by duplication as much as you are trying to say this is a pretty good story based on a computer model kicking out a similar result. I mean, it all sounds pretty good on

Thank you mister Philosophy. This is Physics, where we do not generally speak of "proving" things. But when laymen do use that word, we don't interpret it in the strict philosophical sense which can only be true in Mathematics. Rather we interpret such statements as they were obviously intended, e.g. "Oh, look at these stupid astronomers, just making up stuff; they don't really know anything". When trying to explain to someone making such a statement that they are wrong, (and an idiot), it's kind of ann

It goes like this, when an astronomer tells me something about the universe, or a biologist about the earth's past, they usually put together a chain of evidence in much the same way a detective tries to fit a puzzle together. It's interesting, for sure, but, when a physicist or a chemist tells me something, most of the time it is because THEY BUILT SOMETHING USEFUL. From physics and chemistry come a wide variety of materials and devices,

And in fact, the most spectacular accomplishments of astronomy are when we show that cosmological theories can be found even on good old earth, and vice versa. I present as exhibit 1 the Big Bang. the Big Bang, as I understand it, came from an application of Einstein's GR, coupled with Hubble's discoveries, all together with the insight that the math predicted that there would be some sort of radiation from the event all around us to this day. Thus, some dude puts up an antenna, discovers background no

RTFA! RTFA! RTFA!Nobody has ever thought dark matter explained anything at all that this discovery explains instead. "Perfectly normal" matter does not explain anything that dark matter explains, assuming by "perfectly normal" you mean "baryonic". That is, in essence, the only thing we actually know about dark matter at all: There are things about the universe that cannot be explained by "perfectly normal" matter. If perfectly normal matter sufficed to explain these things, we wouldn't think there was d

Hydrogen and helium are not dust by any definition of "dust" I've ever known an astronomer to use. Dust is, by definition, solid matter which is microscopic, but much larger than atoms. To broaden the term to include plasmas and gases would pretty much make it so broad as to be useless.

Cosmologists use the term 'dust' to refer collectively to non-relativistic matter in the early universe.

In the most basic big bang model, there are only two kinds of matter which we consider: 'dust' and 'radiation'. All non-relativistic matter is treated as a pressureless fluid which we call 'dust', while all relativistic matter is lumped together as 'radiation' and treated as an ultralativistic fluid: one whose kinetic energy is so great that its rest energy is only a small correction to its total energy, and can be neglected (so we can treat them as if they were massless photons).

These definitions aren't used outside of cosmology, so generally you won't hear about them in this context.

Ah, I stand (partly?) corrected. I'm in planetary, which is about as far removed from cosmologists as an astronomer can get. (Seriously, we barely even see each other in the hallways.) I do work with a lot of people who research dust behavior in planetary and galactic contexts, though.:-)

although how the universe's biggest ever black hole could have expanded past its own event horizon is beyond me. But then I'm only a physics grad.

Has it? The "diameter" of the event horizon grows linearly with mass, but an object of fixed density grows with the third root of mass, so as mass increases you'd expect the Schwarzschild diameter to grow faster than the size of the object.

This has zero to do with dark (non-baryonic) matter. They just accounted for half of the missing 'normal' (baryonic) matter that was thought to exist. It's still a small fraction of the total mass-energy sum of the Universe at large.

What was it like, father - what was it like to see the signs, the noodles in the sky... did He.. did He SMILE upon you? Did the Holy Sauce pore through the cockpit insulation as we heard the laymen say?

That's actually pretty cool. I mean, the fact that matter was missing was a bit of a problem. The fact that it's in between galaxies even explains why it was missing. When it's that spread out, it's damn near impossible to see the gravitational effects of it.

Great, except the problem is that we're trying to figure out what we can measure by its gravitational effects but doesn't interact in any other way with normal matter. This is the solution to a different problem.

What was found here was missing __baryonic matter__ the bigger question is still unanswered. Bryonic matter is the normal stuff we are made of but most of the "stuff" in the universe is non-baryonic and still "missing".

(actually, they mention that regular matter is not detected via gravitational effects, they simply observed the absorption spectrum. However, when the gasses are highgly ionized, there are no electrons spinning around waiting to absorb the light, and thus the ionized Hydrogen does not yield an easily detectable absorption. (see 2nd article) "dark matter", non-regular matter, is detected via the gravitational lensing effects. )

It's actually that the atoms are way TOO hot. The oxygens are ionized 5 times. That means that whatever pushed them out there was very violent and hot, and the atoms, even if they were to collide, would never stick.

I'm quoting you so that your explanation is +2 like my incorrect assumption above.

(Sorry for being wrong everyone. That's what happens when you stop studying chemistry at 18 and then forget stuff...)

Wrong. gazeous oxygen will not react spontaneously, but high energy radiation will very rapidly ionize it anyway. On the other hand, ionized oxygen is so reactive it will oxydize the first non-oxydizer atom or molecule it touches, including hydrogen.

In the universe, the only gazeous oxygen we have found yet was created by plants. Without life, it only exists as water, CO2 and various oxydes.

For a long period of time there was much speculation and controversy about where the so-called "missing matter" of the Universe had got to. All over the Galaxy the science departments of all the major universities were acquiring more and more elaborate equipment to probe and search the hearts of distant galaxies, and then the very centre and the very edges of the whole Universe, but when eventually it was tracked down it turned out in fact to be all the stuff which the equipment had been packed in.

To save time, and make sure he didn't miss the kickoff with his buddies down at Cosmic Ray's Space Bar, Father Time swept the other half of the now-missing matter under the rug, so Mother Nature wouldn't find it.

Um, why wasn't the entire EM spectrum scanned across the heavens instead of "discrete" well-known segments like radio, x-ray, visible, IR, UV, etc.? Is it a money and time issue? Otherwise it seems that this should have been found decades ago.

Because different wavelengths require different technologies to detect. Like to detect visible wavelengths you use big mirrors and/or lenses, while to detect radio waves you use antennas, and so forth. It's not as simple as "scanning" the entire spectrum.